A known molten bath-based smelting process is referred to hereinafter as the “HIsarna” process.
The term “smelting” is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce molten metal.
The HIsarna process and apparatus are described in International application PCT/AU99/00884 (WO 00/022176) in the name of the applicant.
The HIsarna process is associated particularly with producing molten iron from iron ore or another iron-containing material.
The HIsarna process is carried out in a smelling apparatus that includes (a) a smelting vessel that defines a smelting chamber and includes lances for injecting solid feed materials and oxygen-containing gas into the smelting chamber and is adapted to contain a bath of molten metal and slag and (b) a smelt cyclone for pre-treating a metalliferous feed material that defines a cyclone chamber and includes tuyeres for injecting solid feed materials and oxygen-containing gas into the cyclone chamber and is positioned above and communicates directly with the smelting vessel.
The term “smelt cyclone” is understood herein to mean a vessel that typically defines a vertical cylindrical chamber and includes tuyeres for injecting solid feed materials and oxygen-containing gas into the chamber and is constructed, so that feed materials supplied to the chamber move in a path around a vertical central axis of the chamber and can withstand high operating temperatures sufficient to at least partially melt metalliferous feed materials.
The smelting vessel includes refractory-lined sections in a lower hearth and water cooled panels in a side wall and as roof of the vessel, and water is circulated continuously through the panels in a continuous circuit.
The smelting vessel also includes a forehearth connected to the smelting chamber via a forehearth connection that allows continuous metal product outflow from the vessel. A forehearth operates as a molten metal-filled siphon seal, naturally “spilling” excess molten metal from the smelting vessel as it is produced. This allows the molten metal level in the smelting chamber of the smelting vessel to be known and controlled to within a small tolerance—this is essential for plant safety.
In one form of the HIsarna process, carbonaceous feed material (typically coal) and optionally flux (typically calcined limestone) are injected into a molten bath in the smelting chamber of the smelting vessel. The carbonaceous material is provided as a source of a reductant and a source of energy. Metalliferous feed material, such as iron ore, optionally blended with flux, is injected into and heated and partially incited and partially reduced in the smelt cyclone. This molten, partly reduced, metalliferous material flows downwardly from the smelt cyclone into the molten bath in the smelting vessel and is smelted to molten metal in the bath.
Hot reaction gas (typically CO, CO2, H2, and H2O) produced in the molten bath is partially combusted by oxygen-containing gas (typically technical-grade oxygen) in an upper part of the smelting chamber. Heat generated by the post-combustion is transferred to molten droplets in the upper section that fall back into the molten bath to maintain the temperature of the bath.
The hot, partially-combusted reaction gas flows upwardly from the smelting chamber and enters the bottom of the smelt cyclone. Oxygen-Containing gas (typically technical-grade oxygen) is injected into the smelt cyclone via tuyeres that are arranged in such a way as to generate a cyclonic swirl pattern in a horizontal plane, i.e. about a vertical central axis of the chamber of the smelt cyclone. This injection of oxygen containing gas loads to further combustion of smelting vessel gases, resulting in very hot (cyclonic) flames. Incoming metalliferous teed material to the smelt cyclone, typically in the form of fines, is injected pneumatically into these flames via tuyeres in the smelt cyclone, resulting in rapid heating and partial melting accompanied by partial reduction (roughly 10-20% reduction). The reduction is due to both thermal decomposition of hematite and the reducing action of CO/H2 in the reaction gases from the smelting chamber. The hot, partially melted metalliferous feed material is thrown outwards onto the walls of the smelt cyclone by cyclonic swirl action and, as described above, flows downwardly into the smelting vessel below for smelting in the smelting chamber of that vessel.
Off-gas resulting from the further post-combustion of reaction gases in the smelt cyclone is taken away from an upper region of the smelt cyclone through an off-gas duct.
The net effect of the above-described form of the HIsarna process is a two-step counter-current process. Metalliferous feed material is heated and partially reduced in the smelt cyclone by outgoing reaction gases from the smelting vessel (with oxygen-containing gas addition) and flows downwardly from the smelt cyclone into the smelting vessel and is smelted to molten iron in the smelting chamber of the smelting vessel. In a general sense, this counter-current arrangement increases productivity and energy efficiency.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.